The development of photonics is expected to lead to the improvement of technology in the future. In particular, photonic crystals (PhC) are intensely attracting interest, since they have promising applications. However, the fabrication of photonic crystals that function in the Visible or near infrared range is a problem still in need of a solution, despite attempts using the latest developments in micro/nano technology.
At present, as a substitute technique of photonic crystal fabrication, laser interference is attracting attention, since laser interference can easily form one-dimensional (1D)/two-dimensional (2D)/three-dimensional (3D) structures with high practical reliability. For example, the diffraction lattice of a one-dimensional (1D) periodic pattern can be formed by interference of two beams, and the diffraction lattice of a two-dimensional (2D) periodic pattern can be formed by interference of three beams as shown in “Formation of a microfiber bundle by interference of three non-coplanar beams” (literature 1).
With respect to a three-dimensional (3D) periodic pattern, recording can be done generally by using four non-coplanar beams (“All fourteen Bravais lattices can be formed by interference of four non-coplanar beams” (literature 2)). In that case, it is thought to be possible to generate intensity distributions of light corresponding to all Bravais lattices by controlling the directions of four interference beams and the polarization of four beams. However, it is very difficult in practice to experimentally realize such a system.
A means which simplifies this complicated system by making possible free selection of the photonic crystal lattice uses an axially symmetric multi-beam interference system, and with respect to many complicated 1D/2D/3D structures, simplification can be realized by controlling the number, phase and intersection angle of beams. One of the advantages of 1D/2D/3D structures formed when the above laser interference is used is that it is possible to express inherently the temporarily and spatially overlapping parts of all interfering beams.
Although it is very difficult to achieve a 3D structure by using particularly extremely short, sub-pico-second pulses, they are thought necessary in order to accelerate non-linear (multi-step, multi-photon or tunneling) absorption to perform 3D recording into a transparent medium. If a periodic pattern of such light intensity can be recorded inside a material, it becomes easy to fabricate photonic crystals of good quality and the templates thereof.
In recent years, some methods were reported to achieve 3D recording in glass, but femto-second pulses were used in these methods. However, these recording methods have been attained by a relatively slow process, such as shot-by-shot scanning. In addition, conventional methods of recording 3D structure by using femto-second pulses necessitate a very complicated optical system of binding three or more light beams of pulses together at one point for interference exposure, since the pulse width of femto-second pulse is short, so that these methods are not practicable.
Literature 1: L. Z. Cai et al., Optics Letters, Vol. 26, No. 23, pp. 1858-1860 (2001)
Literature 2: L. Z. Cai et al., Optics Letters, Vol. 27, No. 11, pp. 900-902 (2002)
The invention of this application has been made in consideration of these circumstances, and aims at solving the prior art problems and providing a 3D holographic recording method of capable of easily forming a 3D periodic pattern in a photosensitive material capable of multi-photon exposure by using a very simple optical system, and also providing a 3D holographic recording system.